Low pH colloidal silica compositions for application to concrete

ABSTRACT

A composition for hardening concrete that has a pH of less than 10, and may have a pH of 8 or less. Thus, the hardening composition may be free of or substantially free of alkaline materials. The hardening composition is water-based and includes silica particles and stabilizer, which may be present on portions of the surfaces of the silica particles. The stabilizer may be aluminum-based (e.g., it may comprise alumina, etc.). In use, the hardening composition is applied to the surface of concrete, either alone, with curing compounds, or as part of a polishing process. Any residue that remains on the treated surface may simply be swept, blown, or sprayed away.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/508,710, filed on Oct. 7, 2014, and titled LOW pH COMPOSITIONS FORHARDENING CONCRETE (“the '710 Application”), now U.S. Pat. No.8,999,056, issued on Apr. 7, 2015. The '710 Application is a divisionalof U.S. patent application Ser. No. 12/366,584, filed on Feb. 5, 2009,and titled LOW pH COMPOSITIONS FOR HARDENING CONCRETE AND ASSOCIATEDMETHODS (“the '584 Application”), now U.S. Pat. No. 8,852,334, issued onOct. 7, 2014. Claims for the benefit of priority to the Feb. 8, 2008,filing date of U.S. Provisional Patent Application No. 61/027,366,titled LOW pH COMPOSITIONS FOR HARDENING CONCRETE AND ASSOCIATED METHODS(“the '366 Provisional Application”) and the Feb. 5, 2008, filing dateof U.S. Provisional Patent Application No. 61/026,427, titled LOW pHCOMPOSITIONS FOR HARDENING CONCRETE AND ASSOCIATED METHODS (“the '427Provisional Application”) were made in the '584 Application pursuant to35 U.S.C. §119(e). The entire disclosure of each of the '710Application, the '584 Application, the '366 Provisional Application andthe '427 Provisional Application is, by this reference, incorporatedherein.

TECHNICAL FIELD

The present invention, in various embodiments, relates generally tochemical compositions and to methods for treating concrete, masonry, orstone, and, more specifically, to chemical compositions for hardeningconcrete, masonry, and stone that have a pH of less than 10, as well asto methods relating to the use of such compositions.

BACKGROUND

When concrete hardens or cures, calcium hydroxide (Ca(OH)₂, or “freelime”) forms in small “deposits” throughout the substrate. Calciumhydroxide is a soft, weak material. Consequently, deposits of calciumhydroxide that are present at surfaces of concrete can, over time,compromise the integrity of the concrete.

Various compounds are known to be useful for reacting with calciumhydroxide to harden concrete, masonry, and stone. These compoundsinclude silicas, silicates, siliconates, and mixtures of silicates andsiliconates. The silicas, silicates, and/or siliconates of thesematerials react chemically with soft, weak calcium hydroxide to formstronger materials, densifying and strengthening the treated surface.

Silicas, silicates, and siliconates are widely available in water-based,or aqueous, solutions. These solutions are typically alkaline, or basic,with a pH of 10 or more. The relatively high pH “stabilizes” thesesolutions by imparting the suspended silica, silicate, and/or siliconateparticles with a negative, repulsive charge that prevents the particlesfrom aggregating and, thus, from falling out of, or precipitating from,the solution. When the pH of a conventional hardening solution dropsbelow 10 (e.g., to 8), the effective negative charge on the particlesdecreases. As a result, the particles no longer repel one another.Instead, they begin to aggregate and precipitate. Stated another way,the solution destabilizes. From the foregoing, it is apparent thatconventional concrete hardeners remain stable over a relatively narrowpH range.

When conventional hardeners that have been applied to concrete, masonry,or stone surfaces puddle, they leave a hard, white residue that isdifficult to remove, often requiring additional chemical treatments,scrubbing, scraping, sanding, polishing, or other labor-intensiveprocesses. As a consequence, an undesirably significant amount of laboris often required to treat concrete, masonry, or stone with conventionalhardeners.

SUMMARY

In one aspect, the present invention includes compounds for hardeningconcrete, masonry, or stone. For the sake of simplicity, the term“concrete,” as used herein, includes concrete, masonry, stone, and othersimilar materials.

Hardening compositions that incorporate teachings of the presentinvention include particles that remain in solution at, or stable over,a relatively low pH (e.g., at a pH of about 3, at a pH of about 3.5,etc.), at a substantially neutral pH, or over a relatively large pHrange (e.g., at a pH of about 4 to about 7, at a pH of about 3.5 toabout 10.5, etc.). Due to the stability of such compositions atsubstantially neutral pH (e.g., at a pH of 8 or less), they also may bereferred to herein as “low pH hardening compositions” or, even moresimply, as “low pH compositions.” The low pH of hardening compositionsof the present invention may be due, at least in part, to their lack orsubstantial lack of alkaline materials, such as sodium or potassium orlithium.

In a specific embodiment, such a hardening composition includesparticles (e.g., silica particles, etc.) and a stabilizer that comprisesan aluminum compound (e.g., aluminum, aluminum oxide (alumina), etc.).The aluminum compound may be present at or on portions of the surfacesof the particles. In addition to the particles and the stabilizer, thecompound may include a surfactant (e.g., an anionic surfactant, anon-ionic surfactant, etc.).

Methods for formulating low pH hardening compounds are also within thescope of the present invention.

According to another aspect, the present invention includes methods forhardening concrete. Such methods may simply include application of a lowpH hardening composition to fresh concrete or fully cured concrete. Insome embodiments, the low pH hardening composition may be applied to asurface of the concrete just before or during polishing.

In another aspect, the present invention includes methods for cleaning asurface of concrete following the application of a hardening compositionto the surface. One embodiment of such a method consists essentially ofsweeping, blowing, or spraying residue of the hardening composition fromthe surface of the concrete to substantially remove the residue from thesurface.

Other aspects of the invention, as well as their features andadvantages, will become apparent to those in the art throughconsideration of the ensuing description and the appended claims.

DETAILED DESCRIPTION

An embodiment of a hardening composition according to the presentinvention includes colloidal silica particles that are suspended in awater-based, or aqueous, solution. A stabilizer, which preventsaggregation of the silica particles and their precipitation fromsolution, may be present on portions of the surfaces of the silicaparticles. The stabilizer may comprise an aluminum compound, such asaluminum or aluminum oxide. In addition to the water, the silicaparticles, and the stabilizer, the hardening composition may, in someembodiments, include a surfactant, which also facilitates suspension ofthe silica particles in the water.

The silica particles remain suspended in the hardening composition at arelatively low, substantially neutral (e.g., pH=6 to 8) or acidic pH. Asan example, the silica particles may remain in solution at a pH of aslow as about 3 or about 3½ and as high as about 10 or about 10½. In amore specific example, the pH of a hardening composition of the presentinvention may be about 4 to about 7. In an even more specific example, ahardening composition that incorporates teachings of the presentinvention may have a pH of about 3½ to about 7.

In various embodiments, the silica particles and stabilizer of ahardening composition may be provided as a colloidal silica suspensionthat includes silica particles having nominal sizes (e.g., diameters) offrom about 3 nm to about 50 nm with an aluminum-based stabilizer.

The colloidal silica suspension available from Grace Davison ofColumbia, Md., as LUDOX® HSA is an example of a colloidal silicasuspension that falls within the scope of the teachings of the presentinvention. That colloidal silica includes a silica content of 29.0% to31.0%, by weight of the solution, with a nominal particle size (e.g.,diameter) of 12 nm and a pH of 3.5 to 5.0.

The colloidal silica suspension may comprise as little as about 5% ofthe weight of the hardening compound for applications in which thesurface that is to be treated is dense, about 15% to about 20% of theweight of the hardening composition when the surface to be treated isnew concrete, or as much as about 50% of the weight of the hardeningcomposition when the surface to be treated is highly porous, as is oftenthe case with old concrete. The amount of silica included in thehardening composition may be tailored to provide the desired treatmenteffect (e.g., hardening, polishing, etc.) without requiring anunnecessarily large number of applications (e.g., more than oneapplication) and while minimizing the amount of residue that remains ona surface after treatment of the surface, or minimizing wastage of thesilica. In some embodiments, the amount of silica may be tailored toleave no residue on the treated surface.

Embodiments of hardening compositions that include surfactants mayinclude an anionic (i.e., negatively charged) surfactant, such asNIAPROOF®, Anionic, Surfactant 08 from Niacet or a non-ionic (i.e., noelectrical charge) surfactant, such as the polyether siloxane copolymeravailable from Evonik Industries' Tego brand of Essen, Germany, as TEGO®Wet KL-245. The surfactant may account for as little as about 0.1% ofthe weight of the hardening composition, or as much as about 2% of theweight of the hardening composition.

Some embodiments of hardening compositions according to the presentinvention may altogether lack a surfactant.

The remainder, or balance, of the weight of a hardening composition ofthe present invention may comprise water.

A specific embodiment of hardening composition that incorporatesteachings of the present invention includes 15%, by weight, LUDOX® HSA,0.5%, by weight, non-ionic surfactant, with the balance (i.e., 84.5%, byweight) comprising water. Another specific embodiment of hardeningcomposition includes 15%, by weight, LUDOX® HSA, 0.3%, by weight,anionic surfactant, with the balance (i.e., 84.7%, by weight) comprisingwater.

A hardening composition that incorporates teachings of the presentinvention may be applied to and allowed to penetrate into concrete.Application of the hardening composition may be effected by spraying,alone or in combination with brushing, or brooming, the hardeningcomposition into the surface to which the hardening composition isapplied. Of course, other suitable application techniques are alsowithin the scope of the present invention.

In one embodiment of an application method according to the presentinvention, the hardening composition is applied to a surface of material(e.g., concrete) that has been substantially cured or fully cured. Priorto applying the hardening composition, any debris is cleared from thesurface to which the hardening composition is to be applied.Additionally, that surface may be planed, honed, and/or polished (e.g.,with a 100 grit (rougher) to 400 grit (finer) pad or polishingcompound). The hardening composition may be applied before or during thepolishing process. Polishing may occur following the application ofhardening composition to the surface, and may continue until, and evenafter, the surface is dry.

In another embodiment of a hardening composition application method, thehardening composition may be applied to a surface of uncured (e.g.,fresh) concrete. As an example, the hardening composition may be appliedwithin thirty minutes following finishing of the surface of theconcrete. In another example, the hardening composition may be appliedwithin about three hours after the surface of the concrete has beenfinished. The hardening compound may be applied to the concrete surfacejust before or at about the same time as any curing compounds areapplied to the surface of the concrete. After the concrete has cured,the surface may be polished.

Once a hardening composition according to the present invention has beenapplied to a surface, penetrated into the surface, and had anopportunity to provide the desired results (e.g., chemically react withcalcium hydroxide) (i.e., the hardening composition has dried), residueof the hardening composition may be removed, or cleaned, from thetreated surface. The residue, which consists primarily of silicaparticles, may be removed from the treated surface simply by sweeping,blowing, or spraying it from the treated surface. No additional chemicaltreatment or labor (e.g., scrubbing, sanding, scraping, polishing, etc.)are required.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some embodiments. Similarly, otherembodiments of the invention may be devised which do not exceed thescope of the present invention. Features from different embodiments maybe employed in combination. The scope of the invention is, therefore,indicated and limited only by the appended claims and their legalequivalents, rather than by the foregoing description. All additions,deletions and modifications to the invention as disclosed herein whichfall within the meaning and scope of the claims are to be embracedthereby.

What is claimed:
 1. A composition for hardening and/or polishingconcrete, consisting of: colloidal silica; a stabilizer for enabling thecolloidal silica to remain in solution at a pH of less than 10;surfactant; and water, the composition being formulated not to form ahard reside on a surface of the concrete.
 2. The composition of claim 1,having a pH of 8 or less.
 3. The composition of claim 1, having aneutral pH.
 4. The composition of claim 1, having a pH of about 3.5 orless.
 5. The composition of claim 1, wherein silica particles of thecolloidal silica have diameters of about 3 nm to about 50 nm.
 6. Thecomposition of claim 5, wherein the silica particles have diameters of12 nm.
 7. The composition of claim 1, wherein silica particles of thecolloidal silica comprise about 1.5% to about 6% of a weight of thecomposition.
 8. The composition of claim 7, wherein the silica particlescomprise about 4.5% of the weight of the composition.
 9. A compositionfor application to a surface of concrete, comprising: colloidal silicaincluding silica particles with sizes that enable the silica particlesto penetrate into the surface of the concrete to react with calciumhydroxide beneath the surface of the concrete; and a stabilizer enablingsilica particles of the colloidal silica to remain in solution at a pHbelow 10, the composition formulated to harden the surface of theconcrete without forming a hard residue on the surface.
 10. Thecomposition of claim 9, wherein silica particles of the colloidal silicahave diameters of about 3 nm to about 50 nm.
 11. The composition ofclaim 10, wherein the silica particles have diameters of about 12 nm.12. The composition of claim 9, wherein the silica particles of thecolloidal silica comprise about 1.5% to about 6% of a weight of thecomposition.
 13. The composition of claim 9, wherein the colloidalsilica comprises from about 5% to about 50% of a weight of thecomposition.
 14. The composition of claim 9, wherein the stabilizerenables the silica particles to remain in solution at a pH of from about3 to about
 7. 15. The composition of claim 9, wherein the stabilizerenables the silica particles to remain in solution at a pH of about 3.5or less.
 16. A composition for application to a surface of concrete,comprising: colloidal silica including silica particles with sizes thatenable the silica particles to penetrate into the surface of theconcrete to react with calcium hydroxide beneath the surface of theconcrete; a stabilizer enabling the silica particles to remain insolution at a pH below 10; surfactant; and water, the compositionformulated to harden the surface of the concrete without forming a hardresidue on the surface.
 17. The composition of claim 16, wherein silicaparticles of the colloidal silica comprise about 1.5% to about 6% of aweight of the composition.
 18. The composition of claim 16, wherein thecolloidal silica comprises from about 5% to about 50% of a weight of thecomposition.
 19. The composition of claim 16, wherein the stabilizerenables the silica particles to remain in solution at a pH of about 8 orless.
 20. The composition of claim 9, wherein the stabilizer enables thesilica particles to remain in solution at a pH of from about 3 to about7.